


dirty little frequencies

by nilchance



Series: ain't this the life [29]
Category: Undertale (Video Game)
Genre: M/M, Rough Sex, Sex Toys, Underfell Papyrus (Undertale), Underfell Sans (Undertale), eventual spicykustard, kustard - Freeform, offscreen fellcest
Language: English
Status: Completed
Published: 2019-07-23
Updated: 2019-07-23
Packaged: 2020-07-12 11:41:48
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 9,176
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19945582
Author URL: https://archiveofourown.org/users/nilchance/pseuds/nilchance
Summary: Red doesn't play fair.





	dirty little frequencies

**Author's Note:**

> detailed content warnings in the endnotes

As soon as Sans stumbles into the kitchen for breakfast, he knows he’s in trouble.

Papyrus greets him with a cup of coffee, a plate of scorched waffles and a cheerful, “Good morning, Sans!”

Sans knows that sweet tone. He’s too tired for this. Either the soul healing isn’t lasting as long as it should’ve because of Gaster and his grabby nightmare hands, Red is right about that sex vampire thing, he has an honesty hangover, or he’s just coming down with a cold or something, but he doesn’t feel great. He takes the coffee. He has a feeling he needs all the caffeination he can get.

As Sans takes his place at the table in front of his waffles and downs a long swig of coffee, Papyrus sits down across from him and continues, “How are you, my dearest brother?”

“You’re laying it on kinda thick,” Sans says. “Did Undyne burn down her house again and now she and Alphys need a place to crash? Did another Sans and Papyrus show up again? Are you dying? Am _I_ dying?”

“No more than everyone is slowly dying!” Papyrus says. 

“That’s a relief,” Sans says. “What do you want?”

“Am I not allowed to show affection and concern?” Papyrus demands.

Sans just looks at him and drinks his coffee.

After a moment, Papyrus sighs and admits, “I might need a thing.”

“Okay.”

“I might need you to do a thing.”

That explains the long windup before the pitch. Money is easy. Doing things, on the other hand…

Considering how much bullshit Sans put his brother through, he owes Papyrus a favor or twelve.

“Okay,” Sans says. It’s a great word, _okay_. Non-committal. “You want me to tell some great jokes? A little juggling?”

Pained, Papyrus says, “Please no.”

Shame. People make some hilarious faces when he starts juggling knives. Sans shrugs. “What d’you need, then?”

“The middle school science teacher quit,” Papyrus says.

“Yeah, Edge mentioned that,” Sans says. 

When he called Toriel to ask about it later, it turned out that apparently the teacher had taken a job with the first integrated monster-human school under the impression that monster kids would ditch their own culture and act just like humans do. No using bullet patterns to express themselves, no battles in the lunchroom to decide who got the last pudding cup, no weirdness to make a nervous human uncomfortable. 

Toriel, who had been halfway through a bottle of wine at that point, Frisk long since in bed, said bitterly that this polite push for monsters to become humans would be the end of them as surely as any war. Sans told her he’d take it over being dusted or shoved back in the mountain at gunpoint. She laughed, and he could hear every year of her long, weary life in the sound.

“Well, the Air and Space Museum has a new exhibit about the way the magical sciences are changing aerospace-y things since we got to the surface,” Papyrus says. “Last night, they called to invite the school to come on an overnight trip to see it, but we have no science teacher? So I thought, well, _you’re_ a nerd who knows science things, especially space and probably air things!”

“Uh,” Sans says, frozen with the coffee halfway to his mouth. “Did you run this by Tori?”

His hopes that Toriel has enough sense to know that him + kids = a lifetime of trauma for everyone involved are dashed when Papyrus says, “You were her first choice! You’re such good friends with Frisk, after all.”

“I tried to kill Frisk at least twice,” Sans says.

“Well, _she_ doesn’t know that,” Papyrus says. “Besides, that was an extreme circumstance! You and Frisk get along just fine in this timeline!”

Sure. It’s not like they’re both painfully aware of the terrible things that they’ve done to each other. No terror or seething resentment whatsoever.

“What about Alphys?” Sans asks.

“In what universe would putting Dr. Alphys in charge of an unruly herd of almost-teenagers be a good idea?” Papyrus asks. “Besides, she has that robotics conference this weekend. She’s giving a talk about prosthetics. Which you would know if you ever checked social media.”

It’s a fair point. Sans has been kind of avoidant since he got back from Edge’s universe, which he could blame on having his shortcuts taken away and that minor thing where he was in crippling pain and also dying. The truth is he’s still just dodging questions he doesn’t want to answer.

Ironic that Red hired him to be a spy/snitch when Sans’s world has shrunk to the park outside the embassy, Red and Edge’s house, and Grillby’s. Back in the underground, sure, he would have no end of interesting info to share, but now...

He keeps finding whole new ways he needs to get his shit together. It’s exhausting. It used to be that the lazy good time boy act was self-perpetuating, but now all those spinning plates have hit the ground and he’s not sure how to glue them back together and start again. Maybe his bullshit was always transparent and the people who care about him just let him get away with it.

“Brother?” Papyrus asks, tugging Sans’s attention back.

“Sorry,” Sans says, pasting on a grin. “The wheel was spinning, but the hamster was dead. Took me a minute to resuscitate them.”

“I’m not sure they make shock paddles that small,” Papyrus says, frowning. “This whole discussion can be tabled, laddered, and chaired if you’re not feeling well. We can find someone else.”

“I’m fine,” Sans says. He fully deserves the skeptical look Papyrus gives him. “When is the trip?”

“They leave Thursday night,” Papyrus says. “Which is when Edgy Me heals you, I know, but maybe if you’re feeling poorly you should do it sooner! Anyway, it would be very helpful of you to volunteer but there is absolutely no pressure. Toriel could always find a lesser science nerd to do it instead.”

Sans smiles. “Careful, buddy. That was almost a compliment.”

“Nonsense! You’re one of the smartest people I know!” Papyrus says with unexpected vehemence.

“Paps,” Sans says, touched despite the instinctive urge to look around to make sure Gaster didn’t hear that and won’t find a reason to tear into them both later. “I’m just a hot dog vendor, y’know? I’m not really--”

Jaw setting, Papyrus continues, “If anybody told you differently, he’s just mad you’re smarter than him and you always were, and--”

Papyrus stumbles to a halt, glazing over. Sans winces, then settles back into his chair to wait while he mentally reboots. When Papyrus comes back, blinking and looking a little lost, Sans says, “You had another glitch, bro. S’okay.”

“Ah.” Papyrus rubs his brow, his eyes squinched at the corners in that way they do when he has a headache. “What was I saying?”

Sans is tempted to lie and move them onto a safer subject, but he’s trying not to lie to his brother so much these days. He’ll save the lies for when he really needs them. “You were telling me how smart I am.”

Papyrus squints at him. “Lack of smarts has never been your problem, brother. It’s always been lack of any common sense whatsoever.”

“That’s more like it,” Sans says. “Would I be babysitting the whole trip or--”

“Oh god, no,” Papyrus says with genuine horror.

Sans snorts. “Wow, don’t hold back, Paps. Tell me how you really feel.”

“You don’t even feed the pet rock!” Papyrus says indignantly. “Toriel volunteered to go. She and a few of the parents would deal with the actual preteen management. You’d just go around the museum with them, ask the tour guide questions, explain sciencey things, etc. You know how to make these kind of things interesting despite science being the absolute worst!”

That sounds like stuff that anybody could do, no Master’s degree in quantum physics necessary. But Papyrus thought of Sans first, like he has faith in Sans’s ability to do this well, and now he’s using the big hopeful eyes. Sans has been able to say no to the puppy eyes once or twice over the span of their lives, but he’s not made of stone.

“Okay,” Sans says.

Papyrus beams. “Really?”

“Sure. Gotta try to convert ‘em to the dark side early,” Sans says. “Besides, what kind of idiot turns down a trip to the Air and Space Museum?”

Delighted, Papyrus comes around the table and hugs him. It’s slightly painful (Sans’s bones ache) but he hugs his brother back tight.

***

As the bus draws closer to Red and Edge’s place, the tension holding Sans together winds tighter and tighter. The world seems slightly too bright and slightly too loud, rubbing him raw. He’s never resented the lack of shortcuts quite so much. Red is going to be an irritant because he always is, he lives to rile Sans up in a thousand frustrating ways, but at least Red’ll get him off.

(Sans wants Red. He wants to climb onto his lap and do things to him that he really shouldn’t be thinking about in a crowded bus, and then he wants to cuddle up and soak in the afterglow for a while because Red’s ruined him.)

Finally, the bus pulls with a skull-rattling shriek of brakes to the bus stop Sans was waiting for. He climbs off and drags his aching bones the couple blocks to Red and Edge’s place. It occurs to him how spartan the house looks, only a glass ashtray on the porch rail to show that anyone lives there at all. He needs to get them a potted plant or something. Catnip. Edge can gather even more strays.

When he unlocks the door, Red is stretched out on the couch with a laptop on his chest because apparently he can’t use furniture without sprawling all over it. There’s a pair of headphones dangling around his neck, like he yanked them off as soon as he heard someone coming. He takes Sans in at a glance and says, “Looks like you need a hot beef injection.”

Sans says, “More like pork. Maybe sausage. You busy?”

“It can wait.” Red puts his laptop to the side and tosses the headphones down beside it. A black and orange paw comes out from beneath the couch to bat at the dangling cord as Red stands. He’s grinning, all lazy heat, and Sans’s quiet desperation ratchets up another several degrees. “So d’you want me to take you to the movies and hold hands, or do you wanna skip to the part where I make you come so hard you black out?”

“Easy, tiger,” Sans says with an amused detachment he doesn’t feel. “Who said you were in charge? It’s my turn.”

Red snags him by the front of his jacket and pulls him towards the bedrooms. There’s a split second where Sans thinks Red might lead him to an unfamiliar one and just fuck him right there in Edge’s bed; in this mood, Sans might actually let him. Red, who’s intently watching his face, quirks a knowing grin and goes for his own bedroom instead.

“Does last time count as my turn?” Red asks as the door closes. He doesn’t seem really invested in the answer, just raising a philosophical question. “You asked me to fuck you.”

Yeah, Sans did. He’d been exposed and raw, off kilter. He needed to reclaim his body; it was broken, poisoned, Gaster’s last experiment, but it was _his_. He could wring pleasure out of it to scratch out that memory of old pain, and who was better at giving him that than Red? 

He was afraid of what he’d do if he was the one in control. He’d been so angry; he wanted to tear Gaster apart. He doesn’t want to hurt Red. (He’ll repeat that as many times as he has to.) So yes, he asked Red to fuck him, and Red made it so good.

It had technically been Red’s turn. Maybe fucking Sans was Red’s plan anyway. But there was no question that Red let him grab the steering wheel.

Sans sighs. “You wanna roshambo for it?”

“Shit yeah,” Red says.

When Red and Edge showed up in their universe, Sans hadn’t unintentionally lost at poker since he was a kid. His streak ended the first time he and Red decided to play. The game lasted for hours and got intense. At one point they decided to drag Edge into it; they put their backs to each other, removing their ability to watch each other’s expressions, and Edge dealt and called their cards. It was the most fun Sans had in years. 

(Okay, and maybe the sexiest thing that had ever happened to him at that point, but whatever.)

He hasn’t lost at rock paper scissors in years either. The whole creepy face-reading thing gives him an unfair advantage, and he’s not above exploiting it. Most of the time it’s not even a conscious decision to win, just a reflex. Which is why it’s kind of hilarious and kind of annoying that their first game ends in both of them throwing scissors. Then rock. Then paper. Then paper again. Then rock. Then…

A few minutes of nothing but ties later, Red says, “I dunno if this is gonna work.”

“Maybe if we close our eyes,” Sans says.

Red scoffs. “Yeah, right, like I can trust you. You’re gonna look.”

“You think I’d cheat?” Sans asks with all the wounded innocence he can muster. “I have such an honest face.”

“We’ve got the same face, jackass,” Red says.

Sans shrugs. “Coin flip?”

He’s got a trick coin in his inventory for times like this, and if Red isn’t smart enough to check, then he deserves to lose.

Amused, Red says, “Tell you what. One more time for all the marbles. If we tie again, we’ll do a coin flip. That sound fair to you?”

It sounds like Red’s figured out a way to cheat, but sure. This ought to be good. Sans says, “Okay.” Then, too fast to give Red time to think: “One two three--”

They both make their respective moves. Sans stares at Red’s hand, which is making the ‘live long and prosper’ gesture, and then at Red. “What the fuck is that.”

“Spock smashes rock,” Red says patiently. “Ain’t my fault you weren’t specific about the rules.”

Okay, that’s an angle Sans probably should’ve expected. If he wasn’t smart enough to think of that as a way to cheat long before Red did, _he_ deserves to lose. Besides, he wants to get to the part where they’re naked.

“Asshole,” Sans says without heat. “How do you want me?”

“Lemme see what you’re working with,” Red says.

Sans does. He’s been ready to go since he got in the door; only his pride kept him from immediately dragging Red onto the mattress. After three days of his own hands and the showerhead, after the way Edge said _I want you_ and the way Red was warm on his lap and all fucked up on endorphins after the flogging, he wants Red with a desperation that would scare the hell out of him if he let himself think about it.

So he doesn’t think about it. Problem solved. 

He lets the diffuse warmth of magic in his pelvis shape whatever the fuck he wants it to, and Red looks him over with satisfaction. Red says, “You like it with a pussy, huh?”

Fuck, Sans is getting ( _boring_ ) predictable. Trying to keep his sudden stab of anxiety out of his expression, he says, “If you want something else, I can try again. I don’t have a preference.”

Red glances at his face, reads his expression in a heartbeat, and grins crookedly. “Right. Forgot your little rule about wanting things.”

“I want plenty of things,” Sans says. “For you to shut up and take your pants off, for instance.”

That grin only gets wider. Red does him one better and takes everything off. He doesn’t move like his bruises still hurt, but Sans asks, “How’s your back?”

With a dramatic roll of his eyes, Red turns, letting Sans get a good look. Red’s shoulders are still crisscrossed with marks. They seem to be healing okay; they’re not that livid scarlet anymore. Red grins at him over his shoulder. “You wanna touch ‘em? Just be gentle with me, senpai. I’m a delicate flower.”

Funny. Red’s back actually reminds Sans of some of Asgore’s orchids, white bone shading to various tones of purple and yellow-green. It’s weirdly beautiful. Hesitantly, Sans runs his fingertips over one of the lighter bruises, barely making contact. The bone is hot to the touch, Red’s 5 HP working overtime to heal him. Red draws in a sharp breath like Sans burned him, and Sans jerks his hand away.

“S’okay,” Red says. “Didn’t hurt. Just sensitive.”

“You sure?” Sans demands.

“I liked it,” Red says, turning so Sans can see in his expression that he’s telling the truth. “Keep touching me.”

So Sans does, too fascinated not to. He’s careful with how much pressure he puts on the bruises as he traces each of them, and Red’s breathing gets heavier. Red’s definitely getting off on this. Within a matter of minutes, he’s flushed. When Sans comes even closer and drags his tongue over the place where most of the bruises intersect, tasting the heat of them, Red shudders. Sans lays his hands on Red’s hips, gripping the bones to hold him in place, and Red laughs a little hoarsely and pulls away.

“Okay,” Red says. His magic is hot and ready in his pelvis. “That’s enough.”

“You sure you don’t want me to steer?” Sans asks.

“Nice try, but no. I won fair and square,” Red says.

“Debatable.”

“Our kind of fair.” Red kneels on the mattress, giving it a little pat. “C’mere.”

Sans sits down on the bed. In one fell swoop, Red grabs him by the soul and drops him on his back. While Sans is busy swearing at him, Red grips his hips and pulls him close until Sans’s pelvis is parked on his lap, his legs on either side of Red, spread open. Sans is suddenly and regrettably much wetter than he was a matter of seconds ago.

“Now I got you where I want you,” Red says.

“I was already going, you dick,” Sans says, his soul pounding with the jolt of adrenaline.

“This was easier,” Red says. Shamelessly, he ogles Sans’s pussy. “Goddamn, you’re pretty.”

“Narcissist,” Sans says automatically.

“Yeah, yeah.” Red palms Sans’s mound in his warm hand, thumb dipping in to find and pet his clit with barely any pressure. It’s maddening. “I was hoping you’d do this.”

“What, call you an asshole?” Sans asks. It’s hard not to push into his touch. His pulse is beating in his overheated magic. “I can do that anytime.”

“I was hoping you’d make a cunt,” Red says with unapologetic bluntness. “I got plans.”

“Is the plan to monologue at it?” Sans says.

Red ignores that, which means Sans wins. “You ever used sex toys?”

Sans gives him his best unimpressed look, which is a little difficult with Red stroking his clit. “My hands work just fine.”

“They sure do, but just because you can use your hands doesn’t mean it’s not fun to do something else once in a while,” Red says. “You wanna?”

At this point, Sans will agree to a lot if it means Red keeps touching him. “Sure, why the hell not. Break out the car battery and the chicken costumes.”

“Maybe later.” Red takes his hand away from Sans’s clit. “Lemme just--”

Red pulls Sans onto his cock, easy with how wet he is. The suddenness of it wrenches a moan out of Sans. This position is too vulnerable. Red can see every expression and shudder.

“Oh, there we go,” Red sighs, his eyes burning hot as he looks down at Sans.

“Change of plans?” Sans asks unsteadily, his thoughts completely scattered by how much he just wants Red to fuck him.

“Tempting,” Red says. “Hold on.”

Sans laughs a little wildly. “I’m on your dick, dude. Where do you think I’m going, exactly?”

“Nowhere,” Red says, looking smug about it. 

He pulls something out of his inventory, a small black bullet linked by a short cord to a controller with a dial. Sans knows a vibrator when he sees one even before Red nudges the dial and makes the bullet hum. 

Red searches his face, looking for an objection, and doesn’t find one. He grins, sharp and (okay, yes, fine, Sans’ll admit it) pretty, and puts the vibrator against the side of Sans’s clit. It’s a little cold. The vibrator purrs against him, deep and rumbly. There’s a moment where his body just isn’t sure what the fuck to do with such an unfamiliar sensation. He’s been fucked in a lot of different ways, but this is a new one on him.

Watching his face, Red says, “That okay?”

“Weird,” Sans says. Between one second and another, his body’s opinion of this shiny new feeling abruptly changes. He draws in a shaky breath. “Good weird.”

Looking pleased with himself, Red strokes his thumb across the curve of Sans’s iliac crest. He seems content to let the toy do all the work for him. Probably a good call. Sans thinks it’d be too much if Red was rubbing it against him. It’s already a lot.

“Are you gonna fuck me?” Sans asks, sounding more desperate than he means to.

“Yep,” Red says, not moving an inch. There’s a slight strain in his voice and his face is flushed. “Fuck, sweetheart, I can feel your cunt twitching.”

Sans shudders, gut-punched by Red’s terrible dirty talk, and turns his face away from that avid stare. The toy is winding him up with embarrassing speed. There’s no gentle, rising pleasure, just a steep slope upwards. He grabs Red’s wrist, not sure if he wants to yank the vibrator away and spare his pride or to hold on so he’s sure Red won’t go anywhere.

"You close?" Red asks, not trying to pull out of his grip. He's so hard inside Sans, something to tighten around, and Sans wishes he would just fucking _move_.

“It’s only been a couple minutes,” Sans says, kicking himself for the way his voice hitched in the middle of what should be a perfectly reasonable statement.

“It’s been three days,” Red says.

He has a point. It’s been three very long days where Sans was riding the edge of agonizing sexual tension when there was another Edge he’d much rather be riding. But he still fights the release that’s creeping up on him quick, holding on by his fingertips even as his breathing gets quicker and he can feel himself pulsing around Red in tight clenches that just wind him up faster.

“Real nice of you to edge yourself for me, honey,” Red says. His voice is a slightly uneven, his grip on Sans’s hip a little too tight. “Take your time. I’m enjoying the show.”

What an asshole.

Sans closes his eyes and deliberately tightens around Red. He’s already so close, but nobody said he had to make it easy on Red to stay still. Red grunts, his hips jerking, a taste of what Sans wants, and Sans may or may not make a pleading noise. If he does, he’ll deny it later.

Then Red moves in him again, a controlled glide in all the wet. Sans shudders hard, grasping at the mattress with his free hand like that’ll help him hold on.

“That what you need?” Red asks, his voice rough. “All right.”

Red fucks into him, slow and easy, just grazing Sans’s g-spot. It wouldn’t be enough to get Sans off most days, but he barely makes it four thrusts. He has enough sanity left to clamp a hand over his own mouth, muffling the noise he makes when he comes. It hits him hard, three days of tension wrung brutally out of him until he’s gasping and wrecked.

(And unsatisfied. It’s like dumping a cup of water on the scorched earth of Hotland and expecting it to cool down.)

In an unexpected show of kindness, Red turns the toy off before Sans has to kick him. Which is good, because Sans isn’t sure he has that kind of control over his limbs right now. Fucking hell.

Red says, a bit of pleased growl in his voice, “I love it when you come on my dick.”

Sans’s first response could be called words if someone was being really generous. Mostly it’s vowel noises. He clears his throat and tries again. “That works out, seeing as you keep getting me off.”

Red grins, all smugness and hunger. Telling him that in a moment of weakness was probably a mistake. “You’re welcome.”

The considerate thing for Sans to do would be to ignore the way this position is already making his spine ache. Maybe he’d let it ride if it didn’t also give Red such a great view of his expression. There used to be a time when Sans really _didn’t_ have preferences because he’d learned to ignore them; he was usually mentally checked out anyway. It’s different with Red.

(Which is probably why Red is the only lover he comes back to.)

Before he opens his mouth, Red says, “You wanna move?”

“Kinda,” Sans admits. “Sorry.”

Red pulls out of him and gives his cheek an affectionate smack. Sans can feel how hard and hot Red’s dick is where it rests against his leg. “Yeah, I’d much rather you throw your spine outta whack for days for dumbass sex reasons. The boss would never let either of us hear the end of it. Now get on your hands and knees. I’m not done with you.”

The casual authority in Red’s voice really shouldn’t make Sans hot, but it does. He pushes himself awkwardly off Red’s lap, getting a good view of the blue streaked and splattered all over both of their femurs. Red takes himself in hand and gives his dick a few lazy strokes, getting blue all over his fingers.

“Maybe you should ask me nicely,” Sans says. Not his best line, but his higher brain functions are still coming back online after his orgasm fried them.

Red grins at him. “Maybe I ought to put you where I want you and just use that sweet cunt of yours until I’m satisfied.”

It’s like Red rooted around in the dirtiest corner of Sans’s subconscious and casually tossed an idle spankbank fantasy out into the light. Sans hesitates just a fraction too long.

Red laughs. “Thought so.”

“All right, shut up, I’m going,” Sans says.

He gets on all fours. It feels almost as vulnerable as the last position, particularly when Red nudges his legs to urge them further apart. He’s on display.

Sans can feel the mattress shift as Red kneels behind him. He’s not prepared for Red to press a hand between his shoulderblades and urge him down. It leaves him bracing himself on his arms with his ass in the air, an echo of the way he once rimmed and then fucked Red. He opens his mouth to object and can’t find a single goddamn reason why. Red can’t see his expression, after all. This is pretty much ideal.

“Problem?” Red asks, as if he’s idly curious.

“Nope.” Sans buries his face in his folded arms and continues, muffled, “Waiting for you to get around to fucking me. Don’t rush on my account.”

Red seems to take him at his word. He runs a hand down Sans’s spine and sighs like he’s enjoying an expensive cigar or single malt whiskey, something to be savored at length.

(Ha. At length. Because dicks.)

Speaking of dicks, he feels the head of Red’s press against his cunt. He takes Red as easily as breathing, although breathing isn’t quite so easy at the moment with Red so deep he’s nearly in Sans’s throat. Red gives an appreciative groan, and Sans shudders with the sound like it reverberates in his bones.

“Why the hell would I rush this?” Red asks. It takes Sans a moment to remember he’d snarked about that, and then that memory scatters as Red starts to fuck him. Slow, still so fucking _slow_ , but deep and at a devastating angle. “You feel amazing.”

Sans keeps his face in the bend of his elbow and grasps the back of his own neck in the other hand, trying to keep it together and knowing he’s going to fail. He’s making little noises with each thrust, not quiet enough.

Red grasps his hip, fingers flexing like a cat kneading. His voice, rough and familiar, is another layer of sensation. “Vibrator’s right by your left knee. How ‘bout you keep yourself busy while I fuck you?”

Sans hesitates, and Red doesn’t push him. Of course, Red also doesn’t move any goddamn faster.

With a shaky hand, Sans fumbles for the vibrator and manages to turn it on. He pushes the bullet against the side of his clit and grunts like he’s not the one doing this to himself. His clit is still a little oversensitive, making the vibration feel even stronger. He presses back against Red like the pleasure is something he can get away from.

“That’s right,” Red murmurs. “Good boy.”

Sans shudders like the words are a hand around his throat. In retaliation, he shoves himself back onto Red’s dick hard enough that their pelvises clack together. It seems to catch Red off guard; he groans like the noise is punched out of him. When Sans goes to do it again, Red holds him still with a casual strength that sends a regrettable wave of heat through Sans. 

“You need it harder?” Red asks. Sans can hear how pleased he is by that, his voice a rough purr. Apparently by trying to be a pain in the ass, Sans played into his hands. Red lets go of his hips, the sudden absence of pressure making Sans feel unmoored. “Go ahead. Take what you want.”

Sans lets out a shaky breath. “You gonna make me do all the work?”

“Yeah,” Red says, completely unapologetic. There’s no yield in his voice. “Fuck yourself on me.”

It’s a game, as much as a hand of poker or a round of roshambo. If Sans said he didn’t want to play, Red would stop on a dime. He’s an asshole, but not about that. Which is Sans’s only excuse for doing what Red asks. 

If Red’s letting him set the pace, then Sans is going to do his best to wreck him even if it means mutually assured destruction. He fucks himself on Red with all the frustrated desire of the last three days. It’s fast and it’s rough, made clumsy by the fact that he’s still grinding the vibrator against his clit, and he can hear Red’s unashamed moans over the smack of magic on magic. The wrecked sounds Red makes almost drowns out Sans’s humiliating awareness of how he must look right now, riding Red’s dick like an animal in heat, muffling his own ragged moans into the mattress.

After the first couple thrusts, Sans can’t stop himself. His aching body seriously protests all this effort, burning with a brutal pleasure that verges on too much, winding tighter and tighter. It’s just a matter of which of them snaps first.

Red doesn’t try to take the steering wheel back. In between wrenching groans, he gasps out, “Gonna wear yourself out for me, Sansy? Gonna lemme fuck you when you’re all tired and sweet?”

Sans makes a thin, shuddery noise he doesn’t recognize.

“Yeah,” Red croons, sensing blood in the water. He reaches around Sans, taking hold of his hand and steadying his grip on the vibrator, making sure it’s on his clit. “I’ll come in you as many times as I want. Till it’s running down your thighs.”

Sans tries to hold out. He tries, but each snap of his hips has him rutting against the vibrator. He’s running out of energy, and Red’s still _talking_ , his fingers just barely brushing against the collar so that it resonates.

“You feel him?” Red asks, his voice fucked out and filthy.

“Yes,” Sans says, helpless and involuntary as breathing. He feels Edge there with them like a warm shadow.

“When I’m done, he can fuck you too,” Red says. There’s a tremor in his voice like he’s as close as Sans is. “I’ll hold you open for him to just--”

Sans comes. No defense against it. It strikes him down, unexpected and blinding, too intense for him to even squeak out a sound. His body locks up. As soon as he falters, Red takes over and fucks him through it. 

Then past it. 

Red’s rhythm is jerky. When the bright surge of Sans’s orgasm passes, overstimulation comes fast on its heels and he grunts a semi-coherent complaint. Red grabs hold of his hips, his grip tight. As soon as Red lets go of Sans’s hand, the vibrator falls through his numb fingers and thrums harmlessly on the mattress. The last of the tension drains out of him all at once, leaving him pliant.

Red’s still moving in him. Taking him. He’s not gentle, but it’s not the frantic pace Sans set for himself. Sans’s cunt feels hot and thoroughly ( _lovingly_ ) used. He’s slick down the inside of his legs with how stupidly wet he is; he remembers what Red said about coming in him again and again, and it manages to wring another shudder out of him.

“Fuck,” Red grits out, using his grip on Sans’s hips to pull him back into each thrust. Sans is okay with that. He’s okay with goddamn near anything, especially since it puts Red at a really good angle. Red groans, and Sans can nearly taste how close he is. “Oh, sweetheart, yeah...”

Another few thrusts, and then the heat of Red’s orgasm rolls through Sans like the tide. His soul feels warm and heavy. His whole body throbs as Red spills into him. He thinks he could come like this if Red kept going, the head of Red’s dick rubbing perfectly and insistently inside him, but there’s no real urgency to the feeling. He’s good.

Finally, Red slows and comes to a stop. He drapes himself over Sans’s back and presses his brow against Sans’s shoulder. They both breathe. There’s a strange wet spot spreading beneath Sans’s ribs.

“You still with me?” Red asks, nuzzling him. His breath is warm against the bone.

Sans gives him a tired thumbs up. After a moment of consideration, he switches to flipping Red off.

“Yeah, you’re fine,” Red says, amused. “Hold on.”

Red pulls out, making Sans grimace as spent magic spills down his femurs. Good thing this is Red’s mattress, not his. A moment later, the vibrator turns off. Red kisses his spine and moves away. Before Sans can decide whether he’s ready to try moving, he feels Red’s fingers spread him open and then Red’s mouth is on him.

“Fuck,” Sans breathes. Red’s clever tongue is on his clit. Sans can’t tense up against it, his body so relaxed the magic between his joints feel like liquid. He’s useless. The lazy, warm pleasure builds in slow waves, as gentle as his last two orgasms were sharp and strong. It doesn’t take long. When he can feel the pleasure about to crash in on itself, he loses his goddamn mind and gasps out, “Red...”

Red purrs, so goddamn smug about Sans calling his name in bed like the worst cliche, and that’s enough to tip him over the edge. Sans comes in his mouth with what he can’t even pretend isn’t a whimper, and Red curls an arm around his hips to hold him up.

When Red’s satisfied, he pulls away and gives Sans’s hip a gentle shove. Sans tips over onto his side and lays there, breathing hard and watching Red wipe his mouth on the back of his wrist. Now there’s two wet spots on the mattress, one silver and one purple. He realizes belatedly that his soul is soaked.

Sans touches his ribs where they’re splattered with soul goo. It’s kind of disgusting and fascinating at the same time. “That’s new.”

Red stretches out next to him, heedless of the wet spots, and appraises at Sans’s soul. Sans gets the feeling that for all Red’s words about how his soul getting wet isn’t a sexual thing, the fact that it made this much of a goddamn mess without Red even laying a finger on it is getting Red off. It means something and Sans doesn’t have the context to know what.

“You’re healing up nice,” Red says. “It was too dry before. Makes it easier to crack.”

Huh. Sans can deal with the squishiness, then. He rubs his chest like he can reach his soul through his ribs. The ache is starting to come back now that the endorphins are wearing off, although it’s definitely better than it was when they started. “If it’s gonna happen every time now, we need to lay a tarp down.”

“This kinda thing doesn’t happen a lot,” Red says. “Not unless you’re actually playing with souls. Then yeah, it can get a little messy. Fun, though.” 

“Why’d it happen now?” Sans asks.

“You must’ve been having a real good time,” says Red, his grin sly.

“Did I, uh, have a soul orgasm or something?” Sans asks. It sounds like a stupid question even as it comes out of his mouth, but it’s not like he’d know. The one Red had didn’t seem like the kind of thing you could miss, but Sans’s soul is defective in a dozen different ways. No reason that subpar orgasms couldn’t be one of them.

“Heh. Trust me, you woulda noticed.” Red touches Sans’s ribs. “Can I taste you?”

For all that Red’s tongue was in his cunt, the suggestion makes Sans instinctively want to cover his naked soul like he has the vapors. “Why would you want to?”

“Just curious,” Red says.

Sans shrugs. “Knock yourself out.”

Without even a pause to say something smartass, Red takes him by the wrist and brings Sans’s fingers to his mouth. He licks them clean, making a little throaty noise when he first tastes Sans. He’s very, very thorough. Sans is pretty fucked out, but the intensity with which Red seems to be kinking on this makes his magic flicker and stir.

With a sigh, Red finally lets him go and licks the remnants off his teeth. His eyes are half-lidded. “Mm. Yeah, I thought you’d be sweet.”

“Goes with my personality,” Sans says dryly, trying to ignore the way his soul is beating fast like it wants to yearn towards Red’s hand.

“I dunno. You can be pretty damn sweet when I catch you in the right mood.” Red lays a hand on Sans’s ribs, gathering up another few viscous drops of soul juice on his fingers and bringing it to his mouth to lick off. “Right after I Fell, I used to lick my soul to keep it wet. Or I jerked off and rubbed the jizz into it. It’s all magic, y’know? Helps it heal faster.”

“Wow,” Sans says, taking those mental images like a brick upside the head. He saw Red touch his own soul, and the thought of him methodically dragging his tongue over it as he slowly comes unraveled is much more attractive than it should be, considering that Sans doesn’t even know how it feels. He just knows that Red likes it, and that’s apparently enough for his libido. “Thanks for the update.”

“I could jerk off on your soul if you wanted,” Red says.

Impressed despite himself, Sans says, “I think that’s the raunchiest thing I’ve ever heard you say and you fuck your own brother.”

“He could be fucking you too,” Red says.

Right, like Sans isn’t painfully aware of that. Something else strikes him, and he sits up. Maybe a touch too fast. He winces at the stab of soul pain, and Red gives him a sharp look. Ignoring it, Sans demands, “What time is it?”

“It’s ‘we oughta move that soul healing up a few days’ o’clock,” Red says. 

Sans waves that off. “I’ve gotta do that anyway, I’m taking some kids on a field trip to DC on Thursday.”

Red’s eyes narrow. “Were you gonna bring that up before you left town?”

“I only found out about it myself a couple hours ago,” Sans says. Red raises a brow, looking eerily like Edge. “Look, Papyrus asked me. There were puppy eyes involved. I’m not proud. So yeah, we’re staying over Thursday night and I’m taking some kids on a tour around the Air and Space Museum on Friday. Other people are actually doing the overnight kid wrangling. I’m just gonna get a cheap motel room or something. Seriously, what time is it? I’ve gotta get to the embassy by one.”

“Wait a sec.” Red gets that feverishly nerdy look in his eyes. “The Air and Space Museum?”

Right. Sans forgot that when he and Frisk went, Red and Edge weren’t here yet. They carved a space so irrevocably into his life that it seems like they’ve been here much longer than nine months. “Yeah. So the humans have this whole thing called the Smithsonian--”

“I know what it is, I’ve read a fucking book,” Red says impatiently. “You’re going?”

“With a herd of twenty preteens,” Sans says. He has a terrible feeling he knows where this is headed. “Chock full of hormones and drama.”

Red cocks his head. There’s that unfortunately attractive light in his eye that he gets when he’s about to manipulate a situation to his own advantage. “Is Frisk going?”

“I dunno,” Sans says. “Paps didn’t say one way or the other. They’re usually at the embassy on Fridays, so maybe not.”

Red shakes his head. “All those other brats get to go on a field trip and Frisk doesn’t? Nah, the queen ain’t gonna stand for that, and Asgore is too scared to piss her off.”

The name makes Sans flinch again, which is annoying as fuck. “So what?”

“Nothing,” Red says airily. “Just thinking out loud.”

The aggressively bouncy notes of Call Me Maybe cuts Red off. His _are you fucking serious_ expression is priceless. Sans snags his phone out of his jacket pocket, and answers it. “Hey, edgelord.”

“Hello,” Edge says. He sounds a little exasperated, and there’s a lot of chatter in the background. “I’m afraid I can’t get out of the office for lunch.”

“Have you tried the door?” Sans asks.

Edge’s sigh comes from the very depths of his soul. “I assure you, I’m laughing on the inside. There was some unexpected news dumped on my lap when I got in the office. I’m sorry for the late notice.”

“Don’t worry about it,” Sans says.

“He needs to rinse off the jizz anyway,” Red says, raising his voice so Edge can hear him.

There’s a long pause like Edge is turning that mental image over in his head. Then he says, his voice rough, “I’ll see you later.”

Sans has nothing particularly good to say to that except maybe _no, stay on the line and read me the phone book in that fucking bedroom voice,_ so he says, “Okay,” and disconnects the call.

“Thinking dirty thoughts?” Red says, chin propped on his hand. “Wanna share with the class?”

“If I keep giving you spank bank material, you’ll get hairy palms,” Sans says. “He says he’s busy. Pretty sure it’s because Toriel told him about the field trip this morning.”

“He’s the guy the king goes to for threat assessments,” Red says. Sans might be the only person who’d notice that underneath his casual tone, Red is a little proud of Edge for that. “He’s probably making a lot of phone calls right now to dig up info. Even if he finds out it’s kosher, he’s a paranoid motherfucker.”

“Can’t imagine where he picked that up,” Sans says.

“Hey, everybody’s paranoid where we come from. The smart ones, anyway,” Red says. “My point is that the boss is gonna wanna tag along to keep an eye on the kid. He’ll probably take a couple of other guards too. And hell, I can do my job anywhere.”

“Just gonna hijack my trip, huh?” Sans asks, amused despite himself by the mental image of Red unleashed on an unsuspecting Smithsonian. “I think Tori might draw the line at you going on the actual tour with the kids after you tried to teach Frisk how to make a pipe bomb.”

“I showed them a schematic of how physics makes a pipe bomb work, not how to actually make one,” Red says, waving that off. “They gotta be at least 13 before I start teaching them how to make explosives.”

“Obviously,” Sans deadpans.

“Besides, me and the queen are cool now,” Red says.

“I think you’re underestimating how long she can hold a grudge,” Sans says.

Red shrugs, looking uncomfortable. “Yeah, well, I dropped off a bottle of hooch on her porch on the anniversary of her kid’s death. One of ‘em, anyway. She busted me and asked me to stick around while she drank it, and we talked about how much her ex sucks. I got a whole lot of info out of it.”

Sans had no idea. The fact that Red’s even admitting to showing that much kindness is a pretty big goddamn deal. 

His shoulders hunching defensively as Sans looks thoughtfully at him, Red snaps, “Eight of her fucking kids died, okay? I’m not a total asshole. Shut your trap.”

“My lips are sealed,” Sans says, zipping his non-existent lips shut. “I’ll take the secret of you being a decent person to my grave.”

Red squints at him, looking more offended by Sans calling him a decent person than the thousands of times Sans has called him an asshole, and then clearly decides to drop the subject. “I ain’t gonna follow you around on your little tour. I’ll wander around the museum on my lonesome and take in the sights. Maybe I’ll get some astronaut ice cream. That shit’s awesome.”

Well, Sans did say he wanted to take Edge on a trip out of town. He gives in to the inevitable. “Fine. Fuck knows what mayhem you’ll get up to if Edge leaves town without you.”

“Oh, there’d be a pile of dusty corpses. I get bored,” Red says. Sans is about 95% sure he’s joking. Maybe 92.5%. “I’ll look at room options in the hotel where the kid’s staying. Maybe we can get a hot tub.”

“Who says I’m staying with you guys?” Sans asks. Red just smirks at him. Sans gives up. “Get two beds. And no honeymoon suites with mirrors on the ceiling.”

“Holy fuck, no,” Red says, appalled. “Are you kidding me? Have you ever seen a goddamn horror movie? I don’t want some creepy little dead girl crawling out of it in the middle of the night and trying to eat my face.”

The thought of Red, who’s just over five feet of murder and fuck you attitude, getting spooked by horror movies makes Sans grin in sheer delight. So much ammunition for mockery, so little time. “Didn’t know you were scared of tiny children, Red. I’ll be sure to change the TV when diaper commercials come on.”

“I’ll stab a creepy little dead girl in the face. It’s just a hassle,” Red says. “Besides, considering that you’re living a horror movie, maybe you better not talk too much shit about taking reasonable precautions.”

It’s a good point. Sans ignores it anyway. “You gonna shower with me, or are you afraid Bloody Mary is gonna come out of the bathroom mirror?”

Red waggles his brows. “Sounds fun. You wash my back, I’ll wash yours. You can rinse your soul reeeeeal slow while we make out a little…”

“Dude, no. It aches like a bitch.” After a moment of consideration, Sans generously adds, “I might be down for that making out thing, though.”

“Thought so,” Red says.

When Red kisses him, Sans remembers too late that Red had been licking up his soul jizz. He tastes himself on Red’s tongue. It’s not unpleasant. Red’s right, it’s a little sweet. He wonders what the magic coating Red’s soul when he touches himself tastes like, and he isn’t sure what to do with the shiver that rolls unexpectedly down his spine at the thought of licking it clean and finding out.

 _Don’t touch his soul,_ Edge said. It’s a straightforward rule. Besides, the odds that Red wants Sans in his head are really fucking low, and Sans can’t blame him.

(Of course, there are always other options. Edge takes his gloves off before touching Sans’s soul because there’s no connection otherwise. Gloves, maybe a dental dam, and--)

Red pulls back and studies his expression. “Why d’you look like you’re thinking about science?”

“I get bored,” Sans says, happy for the opportunity to toss Red’s words back in his face.

“Heh.” Red taps Sans’s ribs over his soul. “You curious? Y’know, if you ask the boss for damn near anything, he’ll give it to you.”

Annoyed with his own transparency and Red’s fucking questions, Sans says without thinking, “That’s funny. He said the same thing about you.”

It’s dangerously close to acknowledging the way their arrangement has changed. Things like Red offering him food, asking him to stay overnight, letting Sans see him when he was half in subspace and vulnerable. Instead of snarling, Red just looks at him like he’s amazed by the depths of Sans’s idiocy. “I’ve been telling you to ask for what you want since the beginning. You think I’m hammering that into your skull for my health?”

“You say that like I know why you do anything,” Sans says.

“You can figure out if some rando didn’t pay a parking ticket fifteen years ago but not that,” Red says, amused. “It ain’t that complicated, sweetheart. I do what I want.”

Says the man who won’t let himself show affection to his brother and only watches hungrily as Sans does it instead. But pointing that out would be dropping a match in a gunpowder factory, so Sans holds his tongue. Instead he says, “Bullshit. It’s plenty complicated.”

Red considers him. “That a problem?”

Hard to tell if Red is just checking in, his whole consent thing, or if he’s actually looking for some kind of reassurance. Reassurance isn’t Sans’s strong point, but he puts a hand on the back of his neck, over the collar. He kisses Red, a quick press of teeth, and says, “Turns out trace amounts of complicated aren’t gonna kill me.”

If he wasn’t touching Red, he doesn’t think he’d feel him relax. Red nuzzles his mouth and then thoroughly gropes his tailbone. “You wanna see if I can get you off in the shower again?”

Sans thinks of that tide of sympathetic warmth he felt when Red came, soothing the nagging ache of his soul, and smiles. “I have a better idea.”

By the time they get out of the shower, he’s gotten Red off twice, Red’s legs are wobbly, and Sans is feeling much, much better.

***

Midnight finds Sans curled up on his mattress, waiting to doze off. He’s been laying here for an hour but his mind won’t stop chasing its own tail. With a sigh, he finally gives up and indulges the impulse that’s been nagging him all night.

Sans should probably try to learn how to bring his soul out without touching it, but hell, it’s not like he minds Red doing that for him. If Red’s gonna insist on sitting in on soul healings to get his voyeur on, he might as well make himself useful. 

Shucking up his t-shirt, Sans reaches under his ribs and gingerly curls his fingers around his soul. This time he’s careful not to hold on too tight. His own touch aches like a bitch but it’s not the searing pain of when he was trying to heal himself.

In the privacy of his own head, Sans can admit that Red is right. His soul does feel softer to the touch. It still seems drier than Red’s, even if it had plenty of juices to marinate in earlier.

Getting it wet helped it heal faster, Red said. Sans can use all the help he can get right now to manage the symptoms until the next time Edge heals him. So he raises the soul to his mouth and gives it a tentative lick.

He knows his soul is fucked up from what Gaster did to it. He’s expecting even the light touch of his tongue to hurt. It does, a little. He’s not expecting the jolt of pleasure that comes with it, not focused in his pelvis but in the whole of him, body and soul. He makes a strangled noise as it shudders through him and then recedes, leaving only aftershocks.

Fuck, that’s intense. No wonder Red looked so wrecked when he touched his soul. Sans didn’t know.

And now that he knows, he’s going to have to sit there while Edge lays two fingers on his soul and try not to wonder what it would be like if Edge wasn’t so careful about keeping his hands still. If Edge just _stroked_...

“Red, you fucking asshole,” Sans mutters.

He thinks Red suggested licking his soul because he was actually trying to be helpful, in his own perverse Red way. That doesn’t mean he wouldn’t also set up Sans to squirm awkwardly through the next soul healing just to entertain himself.

Sans’s soul is already drinking in the wet streak left behind by his tongue, like it’s desperately thirsty for it. He thinks about licking his soul all over, getting it thoroughly wet, and the way his breath shudders out in equal parts want and apprehension is purely involuntary. Then he thinks about the way he couldn’t stay quiet with that one touch and the fact that Papyrus is downstairs, watching TV.

Letting out a slow, deliberate breath, he replaces his soul under his ribcage. When he settles back into the mattress, that ache in his soul is back, but it feels subtly different. More like the frustration of being teased but not satisfied. He’s not sure blue balls is an improvement over his soul trauma symptoms acting up, but this is what he gets for listening to Red.

It turns out that he doesn’t need to lick his soul after all. When he wakes up from a night of restless and incredibly pornographic dreams, his soul is so wet it’s dripping.

**Author's Note:**

> Content warnings: Discussion of anti-monster prejudice at Toriel's school; Papyrus has another moment where he starts to remember stuff about Gaster and has to mentally reboot; Sans has unhealthy ideas about sex; references to childhood medical and emotional abuse; Red talks about teaching Frisk how to make a pipe bomb.


End file.
